ROLE OF INTERFACIAL-TENSION IN NUCLEATION BENEATH MONOLAYER FILMS

Monolayer films at high surface pressures are well-ordered, and due to their 2D crystallinity they can act as sites of preferential nucleati on. Recently it has been demonstrated that films at lower surface pres sures can also be preferential nucleators, despite their decreased ord ering. In this study we show that identifying the factors which can re duce the interfacial tension is vital to understanding the varied mech anisms through which nucleation beneath monolayer films can occur. In particular, the preferential nucleation that is observed at low to med ium surface pressures is explained by the compressible film rearrangin g so as to minimize the lattice mismatch with the nucleating crystal f ace, thereby reducing the interfacial tension of the system. We introd uce a more quantitative approach in this paper to gain a greater insig ht into this phenomenon. The nucleating species must be adsorbed upon the film as a prerequisite for nucleation. We demonstrate that the ext ent of this adsorption may be modeled using the appropriate Pi-A curve s and an equation derived from the Gibbs and Langmuir adsorption isoth erms. This approach also allows values for the adsorption energy and i nterfacial tension for 100% adsorption to be estimated.